import hashlib as hasher
import datetime as date

class Block(object):
    def __init__(self, index, timestamp, data, previous_hash):
        self.index = index
        self.timestamp = timestamp
        self.data = data
        self.previous_hash = previous_hash
        print('-------------', data , previous_hash)
        self.hash = self.hash_block()

    def hash_block(self):
        sha = hasher.sha256()
        line = str(self.index) + str(self.timestamp) + str(self.data) + str(self.previous_hash)
        sha.update( line.encode("utf8")    )
        
        return sha.hexdigest()

def create_genesis_block():
    # Manually construct a block with
    # index zero and arbitrary previous hash
    return Block(0, date.datetime.now(), "Genesis Block", "0")

def next_block(last_block):
    this_index = last_block.index + 1
    this_timestamp = date.datetime.now()
    this_data = "Hey! I'm block " + str(this_index)
    this_hash = last_block.hash
    return Block(this_index, this_timestamp, this_data, this_hash)

# Create the blockchain and add the genesis block
blockchain = [create_genesis_block()]
previous_block = blockchain[0]

# How many blocks should we add to the chain
# after the genesis block
num_of_blocks_to_add = 20

# Add blocks to the chain
for i in range(0, num_of_blocks_to_add):
    block_to_add = next_block(previous_block)
    blockchain.append(block_to_add)
    previous_block = block_to_add
    # Tell everyone about it!
    print( "Block #{} has been added to the blockchain!".format(block_to_add.index) )
    print( "Hash: {}\n".format(block_to_add.hash) )